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I'm restoring a Fiero, "85. It has a reasonably well running 2.8 with automatic. I also have a 2.8 conversion block, crank and pistons(3.1) and everything to change it over. I've had real good luck with a 3.1 conversion I built for my Blazer but this isn't apples to apples. Should I rebuild the '89 Firebird 2.8 block into a 3.1 and lose some compression or stick with the the 2.8 out of the Fiero with 9.5 to one compresssion?
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'86 S10 Blazer 4WD, '87 2.8 with 3.1 crank and pistons, A.R.I. "Stage 2 Cam", Iron Heads with stiffer springs, Holley TBI, Manifold bored to fit the TBI Base(4.3 size), Fiero Covers, MSD Coil, DynoMax Muffler and 2.5 Tailpipe, no cat, Auburn Limited Slip, 3.73 final Drive. 700R. '85 Fiero GT 3.4 Hybrid, relieved top intake and exhaust, 57mm TB, Auto. 3.06 final drive. -
Well none of the 2.8L's had 9.5:1 compression from factory. They were 8.5:1 for low output ones and 8.9:1 for HO and EFI models. The 3.1L comes in at 8:8:1 but you can increase that by zero decking the block which also has other performance benefits. You could also use 2.8L pistons and shave them as discussed in my "Engine Rebuild" thread. Or you could convert to aluminum heads which requires a bit more work but yields the best power output.1993 EXT. CAB, 3.4L V6 TBI, 5spd manual. Sonoma
1990 4Door, 3.2L V6 TBI, 5spd manual. 4X4. Trooper
Because... I am, CANADIAN -
I could swear I saw somewhere that the Fiero had 9:5. I could be be mistaken. What all is entailed by "Decking" the block? Heads and manifold have to be shaved too?'86 S10 Blazer 4WD, '87 2.8 with 3.1 crank and pistons, A.R.I. "Stage 2 Cam", Iron Heads with stiffer springs, Holley TBI, Manifold bored to fit the TBI Base(4.3 size), Fiero Covers, MSD Coil, DynoMax Muffler and 2.5 Tailpipe, no cat, Auburn Limited Slip, 3.73 final Drive. 700R. '85 Fiero GT 3.4 Hybrid, relieved top intake and exhaust, 57mm TB, Auto. 3.06 final drive.Comment
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They machine the top of the block down. It is common practice to bring pistons perfectly flush with the top of the block on almost any engine build. I measured my 3.1L and found on average the pistons were down below the deck 0.012" however I am getting new pistons so the machinist will check with the new pistons before decking the block. You could also avoid machining by getting pistons to correct this but in the 660 world there are not many off the shelf choices like there would be for a small block. Also shaving the heads will make the combustion chambers slightly smaller which will yield more compression. Although you want to keep in mind that taking more than 0.010 off the heads may pose a gasket sealing risk. My heads were shaved 0.005 to clean them up so I calculated a rough 9:1 ratio when all is said and done.1993 EXT. CAB, 3.4L V6 TBI, 5spd manual. Sonoma
1990 4Door, 3.2L V6 TBI, 5spd manual. 4X4. Trooper
Because... I am, CANADIANComment
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aluminum headed,high compression,cammed 2.8 if N/A.OTHERWISE TURBO THAT 2.8.
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